1. Field of the Invention
The present invention relates to a liquid crystal display unit. In particular, the invention relates to a transreflective type liquid crystal display unit to provide high image quality by improving transmittance and to reduce power consumption of backlight.
2. Description of the Prior Art
FIG. 30 is a cross-sectional view to explain an example of arrangement near a pixel of a transreflective type liquid crystal display unit according to the prior art. FIG. 31 is a plan view to explain an example of arrangement near a pixel shown in FIG. 30. This transreflective type liquid crystal display unit comprises one substrate (hereinafter referred as “TFT substrate”) 100 with a thin-film transistor on it and a substrate with a color filter on it (hereinafter referred as “counter substrate”) 200, and a liquid crystal 300 sealed between the two substrates. On rear surface of the TFT substrate 100, a backlight is installed, but it is not shown in the figure.
The TFT substrate 100 has a transparent pixel electrode 108 and a reflective pixel electrode 105 driven by a TFT 102 on inner surface of a transparent insulating substrate 101 made of glass or the like. The reflective pixel electrode 105 is formed on the transparent pixel electrode 108. The transparent pixel electrode 108 allows a transmitting light LT from the backlight to pass, and the reflective pixel electrode 105 reflects external light and turns it to a reflection light LR. Under the reflective pixel electrode 150, a storage capacitor 109 is provided via a gate insulator film 125 between a capacity metal film 124A being in the same layer as the gate electrode 124 of the TFT 102 and a p-Si film 114 being on the same layer as the channel of the TFT 102. The reflective pixel electrode 105 has surface roughness (convex and concave portions) and scatters the external light LR and reflects it in the direction of the counter substrate 200 and turns it to a reflection light LR. In the arrangement as described above, the light from the backlight is interrupted by the storage capacitor disposed under the reflective electrode. As a result, light transmittance is decreased.
The gate electrode 124 and the capacity metal film 124A are covered by an interlayer insulator film 118. Via the interlayer insulator film 118 and the gate insulator film 125, a bus line (=a signal line) is connected to one of the source-drain electrodes of TFT, and the pixel electrodes (transparent pixel electrode 108 and the reflective pixel electrode 105) are connected to the other of the source-drain electrodes via an organic PAS film 106A. An alignment film 110 is disposed to cover the transparent pixel electrode 108 and the reflective pixel electrode 105 to make up the pixel electrode.
The counter substrate 200 comprises a color filter 202, a protective film 203 and an alignment film 204 arranged in this order on inner surface of the transparent insulator substrate 201 made of glass or the like. A light shielding film (black matrix) is generally arranged between adjacent color filter and the alignment film, but it is not shown in the figure. The protective film 203 in the region to match the region of the reflective pixel electrode 105 is expanded into the liquid crystal 200 to reduce the thickness (d) of the liquid crystal 300 to ½ so that the value of Δn·d will be the same for the reflection light LR and the transmitting light LT.
One pixel is formed in a region surrounded by two gate lines 126 adjacent to each other and by two signal lines 127 adjacent to each other. On a part of this region, there is provided a pixel electrode, which has the TFT 102 and comprises a transparent pixel electrode 108 and a reflective pixel electrode 105 driven by the TFT 102. On a portion of the reflective pixel electrode 105, a storage capacitor 109 is disposed. One of the electrodes of this storage capacitor 109 is connected to a storage line 127. In FIG. 31, surface roughness (convex and concave portions) 128 of the organic PAS film 106A are shown.
FIG. 32 is an equivalent circuit diagram of one pixel explained in connection with FIG. 30 and FIG. 31. The same component as in FIG. 30 and FIG. 31 is referred by the same symbol, and detailed description is not given here.
FIG. 33 is a schematical drawing to explain a reflective lens structure in the transreflective type liquid crystal display unit according to the prior art. There is a plurality of projecting blocks 151 made of transparent insulating material in the pixel electrode on inner surface of the TFT substrate 100, and a first reflective film 149 is disposed on it. The first reflective film 149 has an opening at the center of each of the projecting blocks 151, and a second reflective film 150 is formed under each of the openings. A light reflected by the lower portion of the first reflective film 149 is reflected by the second reflective film 150. Then, the light passes through the opening of the first reflective film 149 and is projected in the direction toward the counter substrate 200. In this arrangement, no consideration is given on the arrangement of the pixel electrode, on the arrangement of the storage capacitor, and on display mode of the liquid crystal to improve light utilization efficiency of the light from the viewpoint of liquid crystal driving.
The Patent Document 1 discloses a transreflective type liquid crystal display unit having a reflective lens structure, in which the light beam from the backlight is converged by rear surface of a reflective layer disposed on pixel projection and by the second reflective film and is allowed to pass, thus leading to the substantial improvement of light transmittance. The Patent Document 2 discloses a transreflective type liquid crystal display unit with a storage capacitor on the lower portion of the reflective electrode. Also, the Patent Document 3 discloses a transreflective liquid crystal display unit of transverse electric field type using a transparent storage capacitor.
[Patent Document 1] JP-A-2003-241189
[Patent Document 2] JP-A-Hei-11-101992
[Patent Document 3] JP-A-2005-338256